'78 NM Blackhawk...cyl lockup, endplay, etc.

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kentuckydiesel

Bearcat
Joined
Jun 25, 2014
Messages
1
Hey guys,
I'm new to the forum, but have been shooting Ruger SA revolvers since I was a kid. I have a couple questions regarding my 1978 .357 NM Blackhawk, which I believe has been in the family since new (Dad bought it from my Uncle, then years later, he gave it to me). I carry this gun everywhere, but don't shoot it as often as I would like to.

The other day the wife and I were doing some target practice and I noticed the rear sight blade was popping up on one side. I took it apart to find a couple crushed springs. As things go, I couldn't stop there. I began checking everything out. When I checked the cylinder alignment on lockup, there was a fair bit of slop, and the cylinder always stopped slightly too far clockwise (looking down the barrel). If I rotate it counter-clockwise, it is perfectly aligned, but it always rotates back out of alignment.

Upon tearing it down, I found that the cylinder latch has play, both on the trigger pin, and in the frame slot.

What is the best course of action here? Should I fit an oversized cylinder latch? Shim my existing cylinder latch? BTW, I haven't noticed any shaving.

I can feel a fair bit of play between the cylinder and the base pin. Should this play be there? What are your thoughts on oversized base pins vs new Ruger base pins?

Also, regarding cylinder endplay, If I hold the cylinder back, I am getting about .005"-.006" clearance (hard to tell exactly because of the play between cylinder and base pin. If I hold the cyl forward, a .002" feeler gauge won't come anywhere close to fitting between cylinder and barrel. From what I understand, the .005"-.006" clearance is within spec, but should the forward clearance be as low as it is? Is this too much endplay...and if so, what is the best way to tackle the problem?

Any other recommendations regarding things to work on while it's apart would be appreciated.

Thanks!

-Phillip
 

Carry_Up

Single-Sixer
Joined
Dec 22, 2007
Messages
376
Location
Dallas, TX
kentuckydiesel said:
The other day the wife and I were doing some target practice and I noticed the rear sight blade was popping up on one side. I took it apart to find a couple crushed springs.
Obviously that's a problem and you need to order new parts.
When I checked the cylinder alignment on lockup, there was a fair bit of slop, and the cylinder always stopped slightly too far clockwise (looking down the barrel). If I rotate it counter-clockwise, it is perfectly aligned, but it always rotates back out of alignment.
A valid test and a possible reason for concern. Without examining it and having actual numbers it is not possible to say yes or no. If the chambers CAN move into alignment, then you don't necessarily have a problem.
Upon tearing it down, I found that the cylinder latch has play, both on the trigger pin, and in the frame slot.
Just like every other Ruger single action. If the latch (cylinder stop) did not have play, then your chambers would never line up, unless by a stroke of luck your cylinder and stop were perfectly machined and fitted. The forcing cone does the work of lining up the chamber-to-bore during firing.
What is the best course of action here? Should I fit an oversize cylinder latch? Shim my existing cylinder latch? BTW, I haven't noticed any shaving.
Note you are assuming there should be no play in the latch. Cylinders need to have some rotational play otherwise they won't self-align. You might or might not have excessive play. We can't determine that from a simple description. If you aren't having any bullet shaving, and there is no unusual leading around the forcing cone, then things are working the way they should.
I can feel a fair bit of play between the cylinder and the base pin. Should this play be there?
Depends on exactly how much. The cylinder - especially yours - has to move slightly as the bullet jumps from the throat to the barrel. If you prevent that movement by using a tight stop and larger base pin, then you might start seeing some lead shavings.

Also, regarding cylinder endplay, If I hold the cylinder back, I am getting about .005"-.006" clearance (hard to tell exactly because of the play between cylinder and base pin. If I hold the cyl forward, a .002" feeler gauge won't come anywhere close to fitting between cylinder and barrel.
You might need some narrower feeler gauges. If your b/c gap closes up completely when you push it forward, you have .005" to .006" end play - far too much. b/c gap is fine (.006") Check again. The cylinder slams the rear recoil bearing face on each shot, and with .005" of a running start, wear is accelerated greatly. Looks like a .004" shim washer on the front of the cylinder would correct it.
 
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